I borrowed a baby backpack off my brother when my family went overseas to the UK and Paris for a month. Our DD was 1yo - we used it everyday and it was excellent!!! It went so many places that a stroller simply couldn't- up castle steps, down into Roman ruins. It was so great to use to get around the public transport systems too.
I have not used a backpack since then- and don't think I would use it in everyday life as it can place a strain on your back- especially if your toddler is not a lightweight- But for a short period of time- say a holiday etc- it was invaluable!!!
I think the one my brother bought cost around $100- 150 and it is- Freetime brand. The other thing I like about this backpack is it had a little all weather shade that covered bub and protected her from the wind and sun- and it all folded up and packed away into a little storage pouch when not in use.
Hope this helps